1. Field of the Invention
The present invention relates to an optical pickup used in an optical recording and reproducing apparatus for recording and reproducing of an optical recording medium such as a magneto-optical disk and a method of manufacturing the same. More specifically, the present invention relates to an optical pickup allowing easy and highly-precise positional adjustment of an optical waveguide device and a method of manufacturing the same.
2. Description of the Background Art
When a signal from a magneto-optical disk is to be detected by an optical pickup, a beam from a semiconductor laser is generally directed to the magneto-optical disk. The beam is reflected and split into a beam for detecting a servo error signal and a beam for detecting a magneto-optical signal, and these beams are used for their respective purposes.
FIG. 1 is a plan view of an optical pickup employing an optical waveguide for a magneto-optical disk disclosed in Japanese Patent Laying-Open No. 8-171747, as an example of a conventional optical pickup and its optical system.
A beam 103 emitted from a semiconductor laser 102 fixed on a stem 101 is divided into a main beam and a tracking beam by a grating 104 as a diffraction grating. The beam passes through a hologram 105 and enters a beam splitter 108 formed by adhering a plate glass 106 and a prism 107. The entered incident beam is reflected by a mirror at an interface (surface a) between plate glass 106 and prism 107, passed through a collimator lens 109, reflected vertically by a 45.degree. mirror 110, and collected onto a magneto-optical disk (not shown) as an optical recording medium by an objective lens 111. The beam reflected by the magneto-optical disk passes through objective lens 111, 45.degree. mirror 110 and collimator lens 109 and enters beam splitter 108, where the beam is split into a beam 112 for detecting a servo error signal and a beam 113 for detecting a magneto-optical signal. Beam 112 for detecting a servo error signal enters from beam splitter 108 to hologram 105, where the beam is diffracted, guided by receiving optics 114, and detected as a servo error signal. Meanwhile, beam 113 for detecting a magneto-optical signal is reflected by a mirror surface on a rear surface (surface b) of plate glass 106 forming beam splitter 108, and guided to a coupler portion of an optical waveguide device 115 without passing through hologram 105. The beam coupled to the optical waveguide at this coupler portion is diffracted and divided into a TE (Transverse Electric field) wave and a TM (Transverse Magnetic field) wave in the optical waveguide, guided to an optical detector, and detected as a magneto-optical signal.
Receiving optics 114 and optical waveguide device 115 are fixed on stem 101 by adhesion, housed together with semiconductor laser 102 in one package, and sealed with a cap 116 in an airtight manner. Generally, the position and angle of incidence have to be strictly adjusted to couple a laser beam to an optical waveguide device.
FIG. 2 is a view for illustrating positional adjustment and assembling of the optical waveguide device in the above described optical pickup.
The operation for adjusting the position of optical waveguide device 115 is performed for correctly coupling beam. 113 for detecting a magneto-optical signal to optical waveguide device 115. Optical waveguide device 115 is held so that the relative position of optical waveguide device 115 with respect to semiconductor laser 102 comes to have a prescribed position, and the position of optical waveguide device 115 is adjusted in three-dimensional directions of an optical axis direction Z and directions X and Y orthogonal to the optical axis. After the positional adjustment of optical waveguide device 115 is completed, optical waveguide device 115 is fixed on stem 101 by filling an adhesive 118 in a gap between optical waveguide device 115 and stem 101 while optical waveguide device 115 is held. Taking account of variation in the position for fixing semiconductor laser 102 and variation in the substrate thickness of optical waveguide device 115, the gap is set to at least 100 .mu.m in a normal state so that a variable range for adjustment can be set in optical axis direction Z.
In the conventional optical pickup, however, the position of the optical waveguide device was adjusted in three-dimensional directions of an optical axis direction and directions orthogonal to the optical axis so as to couple a laser beam to the optical waveguide device, and an adhesive was filled in such a gap between the optical waveguide device and the stem that was caused after adjustment so as to fix the optical waveguide device on the stem. As a result, the relative position of the optical waveguide device with respect to the semiconductor laser was offset by shrinkage of the adhesive when it was cured and expansion or shrinkage of the adhesive when temperature changed in the environment where the optical pickup was used. As a result, the laser beam was less likely to be coupled and, in the worst case, the laser beam was not coupled at all and reliability in the environment could not be achieved sufficiently.
After the position of the optical waveguide device was adjusted in three-dimensional directions of an optical axis direction and directions orthogonal to the optical axis, the adhesive was filled in the gap between the optical waveguide device and the stem. Accordingly, the gap between the optical waveguide device and the stem was varied by variation in the position for fixing the semiconductor laser, variation in the substrate thickness of the optical waveguide device, and so on. As a result, the amount of applying the adhesive was not enough to achieve sufficient strength for fixing, or the amount of applying the adhesive was excessive and the adhesive flowed to the surface of the optical waveguide device, reducing the efficiency of detecting a laser beam. Especially, when the optical waveguide device was to be held by sandwiching the side surfaces of the device, the adhesive flowed and attached to the device holding portion, preventing removal of the device. Thus, workability and productivity were lowered.
The optical waveguide device was a semiconductor device formed by laminating an optical waveguide layer on an silicon substrate on which an electric circuit and the like were formed. When the optical waveguide device was directly adhered on the stem, a photo-curing adhesive could not be used as an adhesive. When a heat-curing adhesive was used instead, the optical waveguide device was under thermal stress and therefore the optical characteristics of the optical waveguide device changed or degraded. When an anaerobe adhesive was used, the time for adjusting the position of the optical waveguide device was limited.
Since electric insulation of the optical waveguide device from the semiconductor laser and the receiving optics was unreliable, the optical waveguide device was influenced by other circuits, and the S/N ratio of a magneto-optical recording and reproducing signal was worsened.